The present invention relates to a polycentric variable axis hinge for use, in particular, but not exclusively, in knee braces intended to reinforce an injured knee joint.
The human knee is acknowledged as one of the weakest joints in the body. It is the articulating joint between the thigh and calf muscle groups, and it supports the weight of the body while a person is walking or running. The joint is held together by two small but strong ligaments, namely, the anterior and posterior cruciate ligaments. Knee instability arising out of cartilage damage, the ligament strain and other causes is relatively commonplace since the knee joint is subjected to significant loads during the course of almost any kind of physical activity requiring the use of the legs.
The thigh and legs of the human body are articulated to each other through the knee joint of which the principal motions are extension and flexion by rotation about a horizontal axis extending across the knee in a medial-lateral direction. These motions are complex because they take place about a rotational axis which is not fixed, as is the case with the elbow, but which shifts slightly across the knee in the anterior-posterior direction.
It is important for an adequate knee brace to follow the shifting path of the rotational axis of the knee as closely as possible, and accordingly the principal objective of the present invention is to provide a knee brace hinge which is capable of fulfilling such a criterion.
Additionally, and particularly in the case of injured or weak knees, means must be provided in the hinge of the knee brace to control the extension of the knee joint and to stop the extension, for example, short of 15%-5% of full extension, so as to prevent of knee ligaments injuries. Another objective of the invention is to provide a knee brace hinge, which incorporates improved stop means that may be adjustable to tailor the hinge to individuals, to control the extension of the knee joint and to stop the extension at a predetermined degree of full extension.
In U.S. Pat. No. 4,773,404, and its parent U.S. Pat. No. 4,723,539, and in U.S. Pat. No. 4,890,607, a multi-axis controlled motion knee hinge is disclosed. The hinge is constructed to constrain the tibia to slide rearwardly relative to the femur for a predetermined distance throughout an initial range of flexion of the knee from a straight leg position, and beyond that initial range of flexion, to rotate relative to the femur along a predetermined arcuate path.
In the construction of the hinge described in U.S. Pat. No. 4,890,607, the end portions of femoral and tibial lengths are interconnected by a cam assembly comprised of a pair of cam slots in one of the links and cam follower pins mounted on the other link and engaging the slots. In the particular construction described in U.S. Pat. No. 4,890,607, each slot has a straight segment adjoining an arcuate segment of equal radius. The variable axis hinge of the present invention is of the same general type as the hinge disclosed in U.S. Pat. No. 4,890,607, but it is constructed in a manner such that the hinge more closely follows the actual movement of the knee, as the leg is bent in the rearward direction.
Accordingly, a general objective of the present invention is to provide an improved multi-axis controlled hinge for an orthopedic knee brace which is constructed to have the ability accurately to replicate the complex movements of the knee of a wearer, as the leg is moved.
Another objective of the invention is to provide such an improved multi-axis hinge having relatively high integral strength, as well as tolerance precision and production efficiency.
Yet another objective of the invention is to provide such a variable axis knee brace hinge which is constructed in a manner that enables integration into the hinge of a stop for limiting the range of movement of the leg, and one which may be tailored for individual wearers.
The foregoing objects of the invention are achieved in accordance with a preferred embodiment, wherein a knee brace hinge mechanism is provided which utilizes first and second variable radii camming slots and corresponding cam pin followers, wherein one of the camming slots serves to provide the anterior motion of the upper portion of the hinge, while the second camming slot provides for the unicentric phase of the hinge artarokinematics. During the initial range of motion, pivoting occurs through a short multi-radii slot segment about one of the cam pin followers disposed within that slot. After that cam pin follower reaches the anterior end of the slot, it serves as the axis of rotation or pivot point for movement of other cam pin followers along the second variable radii slot. Such a construction provides an increase in tolerance precision, a precise following of the complex motion of the knee joint, and forceful action of the hinge through the entire range of motion.